A Nether Case is an object created by ports to keep objects safe from harm or usage. They use a pocket dimension to store objects in, temporarily keeping them out of the dimension. This causes the object ot not be summoned or taken out of the Nether Case without it being open. The only way to open a Nether Case is to use the Nether Key or know the given password created by the Port who conjured it. The first Nether Case was brought into existence by a Port named Derek.
One of the most common uses for the Nether Case, is to store a Spirit Object in them. However, other important object are also stored in one. It is also currently believed that the Elixir of Life is in one, which is why nobody can sense it.